This invention has to do with a fluid coupling for use on diesel engine-driven mobile equipment such as wood chippers, rock crushers, road surface grinders (also known as scarifiers or road millers), and the like comminuting mills. This comminuting mill equipment is typically used in conjunction with feedstock conveyors, or in the case of the road surface grinder, used in conjunction with a method to move the grinder along the road to be ground. For controlling the speed and connecting and disconnecting the mills and engines, there are four types of clutch in common use. Three types can be engaged and disengaged with the engine running: a mechanical clutch, a hydraulically operated mechanical clutch, and a fluid coupling. One type must be engaged with the driver stopped and it is usually disengaged with the driver running: a mechanical torque limiter. The feedstock conveyors, or driving mechanisms of road grinders, are typically driven separately by hydraulic motors via hydraulic pumps that are mounted on and powered by the diesel engine, the conveyors being controlled by a manual control valve remotely operated by the operator of the mobile equipment. Heretofore, with a mechanical clutch, the conveyors have been run at a constant speed that may be set by the operator or at a speed that is directly proportional to engine speed. Because the hydraulic pumps and motors are positive displacement; if a jam develops in the mill, the operator operates the control valve to the reverse position, the feedstock conveyor stops and backs up for several seconds at the same speed as it goes forward, and then when the operator observes that the mill is cleared, the operator manually puts the valve into forward position and the conveyor returns to a normal forward feeding rate. A problem with this combination of a mechanical clutch and a manually operated conveyor or road grinder is that the operators reaction time is slow, compounded because the operator has much equipment to operate simultaneously, and therefore, it is relatively easy to jam a mill to a complete stop. If such a quick and immediate stop occurs, the diesel engine, especially certain susceptible components, such as turbochargers, can be expected to be damaged, often requiring repairs before restart.
These problems of damage to the diesel engine and its susceptible components are generally tolerable when the diesel engines being used are only up to 300 hp. However, the problems that result from a quick and immediate stop are exacerbated as the diesel engine sizes increase to the current levels of 1000 to 1500 HP and as the new electronically controlled fuel systems are introduced that measurably increase the power ratings of diesel engines without significantly changing the physical size and without significantly changing the physical strength of the engines.
Mechanical clutches have been widely used in such diesel engine driven mobile equipment applications. A mechanical clutch mechanism, such as manufactured and supplied by Twin Disc, Inc. of Racine, Wis., is mounted onto the flywheel housing of a diesel engine. In such a manually operated mechanical clutch, a lever is used to operate the clutch pack and requires an operator to be next to the diesel engine and clutch housing while engaging and disengaging the clutch. This arrangement functions reasonably well except when a very hard object or a large amount of feedstock is fed into the comminuting mill, for example, a hammer mill, and the hammer mill becomes overloaded and jams. In this case, the belts driving the hammer mill slip and wear, the bearings become overloaded, and the diesel engine stops almost instantaneously. This damages the bearings, the belts, the clutch, the diesel engine, and the turbocharger for the diesel engine.
As a mechanical clutch is used over time, the surfaces of the clutch plates wear and the linkage needs to be adjusted to make certain the clutch can be fully disengaged at one end of the clutch lever throw and fully engaged at the other end of the clutch lever throw. If the clutch cannot be fully disengaged, then a considerable amount of power can still be transmitted and the clutch plates will get very hot and possibly become severely damaged. If the clutch cannot be fully engaged, then the clutch will slip at high-power conditions and wear rapidly. Because lever activated mechanical clutches require the operator to be situated very close to the diesel engine, clutch, sheave and belts or other load equipment when the lever is actuated to engage and/or to disengage the load equipment, if the high-powered mechanical equipment breaks, parts may be thrown about and pose grave risk to the operator. Hydraulically operated mechanical clutches that use a lever operated master hydraulic cylinder and a slave hydraulic cylinder to operate the clutch permit the operator to be further removed, but the rest of the problems remain.
Another version of an hydraulically actuated mechanical clutch is one wherein the mechanical clutch pack is compressed and thereby engaged by means of hydraulic pressure, and the hydraulic pressure is controlled by an electronic controller, such as manufactured by Power Transmission Technology, Inc., of Ohio. In normal operation, the electronic controller, which is remote from the clutch, can be manually given a signal to engage, and the controller causes hydraulic pressure to act, engaging the clutch. Similarly, a manual signal to the controller can cause the hydraulic pressure to be released, and the clutch pack is released and almost no power is transmitted through the clutch. Under abnormal conditions such as a jam that develops over several seconds, the electronic controller, essentially a dedicated digital computer based controller, can sense a decrease in speed, and the controller can release the clutch pack and attempt to reengage the clutch a series of times. After a preset number of attempts to reengage the mill wherein the speed of the output shaft of the clutch does not increase to engine speed, the electronic controller will decide that the mill is jammed, and the controller can cause the clutch pack to remain released. In summary, this type of electronically controlled, hydraulically actuated mechanical clutch (a) in the case of a jam that develops over several seconds, can separate the engine from the mill when the mill is jammed, saving the engine and its susceptible components from damage, but, in the case of an instantaneous jam, cannot separate the engine from the mill fast enough to avoid stopping the engine and damaging susceptible components, and (b) can sense when there is too much wear of the clutch parts to assure full engagement, and can separate the engine from the mill in this case, or once separated, can maintain separation of the engine from the mill. However, this type of hydraulically actuated mechanical clutch suffers from the problem of all mechanical clutches: From time to time and depending upon operator care and the types of duty to which the mill is subjected, the transmission must be disassembled and the worn clutch plates must be replaced.
For lower power equipment, below perhaps 300 hp, mechanical clutches do not wear much during normal engagement and normal disengagement. However, as the power transmitted increases to the current levels of 1000 to 1500 hp, the wear of mechanical clutches during normal engagement and normal disengagement increases to the point that it is noticeable and is a concern. Due to the wear during normal engagement and normal disengagement, and due to the possibility of shearing shafts and couplings during a quick engagement event and throwing these parts about, it is common practice for manufacturers of all sizes of mechanical clutches to provide signs to be mounted on the equipment and visible to the operators, that the clutches must be engaged when the engine is operating at idle speed, and not above idle speed, and particularly, not at the normal running speed which is well above idle speed.
In recent years, mechanical torque limiters have been introduced and used to separate the engine from the mill in the case of a jam in the mill. A mechanical torque limiter is a mechanical device that can be mounted on the end of the output shaft of the mechanical clutch in direct drive arrangements. They can also be used with side load applications, and they function as described here. In a mechanical torque limiter, a housing part mounted on the driving shaft contains a series of radial or axial pins backed by springs and the mating part, a driven part, is attached to the driven shaft; this driven part having detents into which the ends of the pins are seated. The housing part and the driven part are held concentric to each other by rolling element bearings. When an over torque condition occurs, the pins slide up from the bottom of the deep-end groove and the springs overload and functionally break away, causing the two parts of the mechanical torque limiter to separate mechanically so that torque can no longer be transmitted from one part to the other part. For safety, the springs and pins of the mechanical torque limiter are retained in the housing part. After the driver is stopped, the springs and pins of the mechanical torque limiter can be manually reset. After the hammer mill is cleared, the diesel engine can be started and the equipment put back into service. The pins, detents, and rolling element bearings do experience some wear during each separation event, and therefore, they can be expected to require reconditioning maintenance from time to time, with the frequency in proportion to the severity of the duty.
Fluid drives for stationary equipment have been in service for several years, with the earliest ones being developed in approximately 1905. Three well-known manufacturers of this equipment today are Turbo Research, Inc (of the USA), Voith (of Germany) and Transfluid (of Italy). Three broad categories are (1) variable speed fluid drives, (2) constant speed fluid couplings that, after the start-up period on the order of seconds, have no means for any significant variance of the output speed which is slightly less than the speed of the driver, and (3) fluid couplings for which the output speed is either nearly zero or slightly less than the speed of the driver, and can be repeatedly cycled between these two states by operation of an oil flow control valve which controls the flow of circuit oil, respectively, by either bypassing oil to the reservoir in the “off” state or by directing oil to the fluid coupling in the “on” state. Such a control valve may also be referred to as a diverter valve.
Variable speed fluid drives of type (1) above are described in U.S. Pat. Nos. 5,331,811, 5,315,825, and 5,303,801, and are manufactured by Turbo Research, Inc. and Voith. These patents are referenced to provide extensive background on fluid drive technology, since variable speed drives are not the subject of the present discussion.
Fluid couplings for stationary equipment identified as type (2) above have been in service for several years, particularly on stationary motor driven equipment, such as mills and conveyors. Two well-known manufacturers of this type are Voith (of Germany), and Transfluid (of Italy), represented by Kraft in the USA.
One of the most common forms of type (2) fluid couplings is self-contained, and has all of the circuit oil stored in it. One part of the fluid coupling, the impeller and impeller casing assembly, which forms the entire outer shell, is mounted on an end of a motor shaft. The driven portion, including a runner, is mounted onto the shaft of the driven equipment such that the runner is inside the impeller and impeller casing assembly. These fluid couplings, which are almost invariably designed and manufactured with the impellers, runners, and casings made from aluminum for reasons which include lower weight and lower cost, have a series of fuse plugs mounted in the outer periphery. These fluid couplings are intended to be used for “soft-start” conditions, and are not expected to be used where jams are to be encountered, though occasionally jams are encountered. Often this type of fluid coupling has two functional chamber for containing oil, one chamber containing most of the oil when the fluid coupling is stopped, and a second chamber which is the fluid coupling chamber that contains the impeller and runner vaned structures used for transmitting torque from the impeller to the runner. Once the motor is started, oil moves from the storage chamber to fill the fluid coupling chamber containing the impeller and runner with oil and the oil can not be removed from the fluid coupling chamber without (a) either shutting down the motor or (b) opening (melting) the fuse plugs. When this type of fluid coupling is stopped under normal circumstances, the oil drains from the fluid coupling chamber back to the storage chamber. When in operation, heat is generated in the fluid coupling in proportion to the slip speed between the input shaft speed and the output shaft speed, and the slip speed increases in direct proportion to the torque transmitted. In normal operation, the cooling fins that are cast into the outer surface of the impeller and casing dissipate to the surrounding air the heat generated by the fluid slip process. Should the equipment become overloaded, or the load equipment jam, much heat will be generated in the oil and in order to protect the load equipment as well as to protect the aluminum parts of the fluid coupling from failing, the fuse plugs will melt, permitting the oil to be spewed out of the rotating impeller casing until empty, and this separates the load equipment from the motor, and the motor will operate essentially unloaded until it is shut down. Several gallons of very hot oil typically are spilled in such an event. This is dangerous for personnel in the area, can be a fire hazard, and, today, depending upon the amount of oil spilled in such an event occurring in the United States, it may well be a reportable event to the United States Environmental Protection Agency (EPA). Due to these safety and environmental issues, Turbo Research, Inc. has not manufactured this type of equipment.
A subsequent version of this equipment by Voith, and Transfluid for use with mobile equipment included a sealed external housing around the rotating element and oil circulating pumping and cooling equipment. The fluid coupling impellers, runners, and casings are still made from cast aluminum with the vanes being thin, and the impellers or impeller casings contain the fuse plugs so that during an overload event the fuse plugs melt, the oil spews out of the rotating element limiting the temperature to which the aluminum parts are exposed and the duration of the exposure, but the oil is contained in the sealed external housing and is not lost. The diesel engine can be stopped under a controlled stop sequence without damage. However, in order to be able to run again, the external housings of this design have to be opened and the fuse plugs have to be replaced. The fuse metal is contained somewhere in the oil reservoir, and unless the reservoir is completely cleaned out, the fuse metal can be drawn into the oil pump with the normal suction oil flow, and therefore, potentially, the fuse metal can pose problems to the oil circulating pump.
Fluid couplings of type (3) above are the primary focus of this document. Turbo Research, Inc., Voith and Transfluid have developed fluid couplings which can be turned on and off by changing the state of an oil flow control diverter valve, usually an electrically operated valve such as an electric motor operated valve or an electrical solenoid operated diverter valve. Some of the Voith and Transfluid fluid couplings use fuse plugs in the outer periphery of their fluid couplings and these fuse plugs melt during an over-temperature event, and must be replaced by opening the external housing, or at least by opening a port in the external housing. Turbo Research, Inc. fluid coupling design uses an over-temperature switch to continuously monitor the circuit oil temperature as it discharges through a series of orifice holes at the periphery of the impeller or impeller casing, and in response to an over-temperature condition, this over-temperature switch causes an electrically operated diverter valve to divert circuit oil from going to the fluid coupling element and to bypass the circuit oil flow stream to an oil reservoir. After such an over-temperature event occurs, the fluid coupling chamber evacuates, and the diesel engine can be caused to idle, which gives the various elements of the fluid coupling a period of time in which to cool gradually, avoiding excessively high thermally induced stresses, particularly in the components of the rotating element. Voith and Transfluid also incorporate the function of an over-temperature switch to monitor the circuit oil as it discharges from the circuit, though there may well be a different method of effecting this function, and such switch causes an electrically operated diverter valve to change state as described above upon sensing an over-temperature condition. With a fluid coupling in operation instead of a mechanical clutch, as the mill becomes overloaded, the output speed of the fluid coupling and the speed of the mill decrease substantially and in direct ratio to each other, while the diesel engine speed either remains constant or declines to a limited degree, but the diesel engine does not stop. In the case of a fluid coupling and a manually controlled feedstock conveyor, as above described, the reaction time of the operator is still slow, and therefore, it is still easy to jam a mill to a complete stop. However, with a fluid coupling with a circuit oil discharge temperature sensing device in service, if the circuit oil discharge temperature does increase above the pre-set trip point as occurs when the mill, the output shaft and attached runner stop, and the diesel engine and attached impeller will continue to rotate, while the fluid coupling system shuts down with no damage to the engine or to its components.
Turbo Research, Inc. developed fluid couplings with heavy duty steel impellers, runners, and casings so that these fluid couplings can be engaged and disengaged at any engine speed, including full engine operating speed, and can survive undamaged more severe over-temperature events than can be expected from fluid couplings made with cast aluminum components, particularly those having cast aluminum components with thin vanes. Experience with the Turbo Research, Inc. fluid couplings indicates that if the mill was not cleared and therefore is still jammed at the time that the fluid coupling is engaged, the circuit oil will get hot, the over-temperature switch will detect this and will trip the circuit oil control valve so that the circuit oil is diverted, and the fluid coupling returns to the disconnected state, with no damage to the fluid coupling or to the drive train.
Today many fluid couplings are designed with some means for continuously monitoring the circuit oil as it discharges from the element, with over-temperature switches, and with electrically controlled circuit oil flow diverter valves, and have no wearing parts such as the mechanical clutches have, have no resetable springs and detents such as the mechanical torque limiters have, and have no fuse plugs such as were previously used in the Voith and Transfluid fluid couplings. For this reason, it has been shown that the fluid couplings with the over-temperature switches and oil diverter valves are the lowest maintenance clutch means available.
One advantage of the fluid coupling over a mechanical torque limiter is that occasionally there are lumps in the feed stock entering the hammer mill that are big enough to cause a mechanical torque limiter to separate, even when set to separate at five times rated torque, but which can be chewed up and processed with a fluid coupling because the fluid coupling continues to transmit power in a substantially overloaded condition for some period of time. During the time period of this overload condition, the temperature of the circuit oil and of the fluid coupling continue to increase, but in that time period, hard lumps, if not too large or not too many, will be processed and the comminuting mill will clear itself. If the mill does not clear itself by the time that the circuit oil discharge temperature reaches the trip set-point, the over-temperature switch causes the circuit oil to be diverted to a reservoir, and the impeller-runner cavities will empty, thus reducing the torque transmission of the fluid coupling to a minimum, so that the diesel engine becomes unloaded and can be shut down in a normal shutdown method without damage, so that in this manner, the fluid coupling functions as a torque limiting device.
In some cases, the mobile equipment drive train can be assembled with a fluid coupling driven by an engine, the fluid coupling driving a mechanical torque limiter, the mechanical torque limiter in turn driving the mill, for the specific purpose of having the fluid coupling benefit of being able to chew through overload conditions as well as for having the mechanical torque limiter benefit of minimizing damage to the mill should a large chunk of steel enter the mill and be hit by a hammer causing a great impact sufficient to separate the parts of the mechanical torque limiter immediately thereby instantaneously terminating the power to drive the mill.
Voith and Transfluid typically manufacture the external stationary housings for their type (3) fluid couplings either as complete castings or welded fabrications including the oil reservoir, and they use a bearing arrangement with a bearing between the housing and the input end of the input shaft, two shaft bearings between the input and output shaft assemblies to resist side loading, and one bearing between the housing and the output shaft, so that one output shaft can be used for dual purposes: (a) mounting a flexible coupling hub for direct drive, or (b) mounting an overhung sheave with side loaded belts that does not require and does not permit a support bearing on the outboard end of the sheave. The Voith and Transfluid design with a bearing supporting the input end of the input shaft requires some form of radial flexibility between the input shaft of the fluid coupling and the flywheel of the diesel engine because there are substantial radial runouts in the nominal design of diesel engines, and consequently, this design uses a form of a Holset coupling with elastomeric elements between the coupling part fixedly mounted to the flywheel and the coupling part fixedly mounted to the input shaft.
Turbo Research, Inc. developed a fluid coupling module that can be used with, and bolted to, any of several output power train assemblies such as, for example, clamshell with sheave and outboard bearing for side loads, direct drive housing with outboard bearing, parallel offset gears and gear housing, and right angle gears and gear housing, wherein each fluid coupling module and output drive train assembly use the appropriate output shaft for the fluid coupling runner and the specific drive train selected. Further, the Turbo Research, Inc. fluid couplings are designed with a bearing arrangement having two high capacity bearings supporting the output shaft and, in the case of the side load drive train, straddling the sheave or gear, and the inboard end of the output shaft, which is overhung into the fluid element cavity, supports one inter-shaft bearing to one end of the input rotating assembly. In this design, the input end of the input shaft, impeller and impeller casing assembly is supported by a series of thin flexible diaphragms that, near the outer periphery, are fixedly bolted to the diesel engine flywheel, and near the inner edges, are fixedly bolted to the input shaft, providing axial and angular bending flexibility between the input shaft of the fluid coupling and the diesel engine crankshaft and flywheel assembly, and therefore, in this arrangement, the bearings of the diesel crankshaft functionally support the input end of the fluid coupling input shaft and impeller assembly. The advantages of this design include (a) the ability of the large straddle bearings of the output shaft to handle repeatedly extremely large side loads concomitant with a jam of a mill, (b) a very substantial reduction in overall length provided by the use of a flexible diaphragm disc coupling instead of a Holset style coupling between the flywheel and the fluid coupling input shaft, which is beneficial to those applications where the axis of the engine and fluid coupling drive train is transverse the mobile equipment trailer, and therefore, perpendicular to the length of the drive train, and (c), due to (b), a reduction in the overall trailer width, reducing or eliminating the need for special permits for the trailer to travel on the highways.
The diaphragm discs used in the subject fluid couplings are adapted from diesel engine driven electric generators made by Onan of Minnesota, in which application the diesel engine crankshaft and crankshaft bearings support through the flywheel and disc-pack the inboard end of an electric generator. Individual discs are on the order of 0.040 to 0.060 inches thick, and multiple discs are used in a disc pack, the number of discs depending upon the torque transmitted. The discs are made by a stamping process using accurate dies, and are commercially available. Such disc packs are radially stiff, have limited flexibility in relative axial displacement between the connected shafts, and are quite flexible in angular bending between the connected shafts. Similar disc packs are used in a variety of flexible couplings connecting two adjacent shaft ends, are available in many sizes, are sold under the trade name of Thomas, are made by Rexnord, and are also commercially available. The application of a flexible disc-pack to a fluid coupling driven by a diesel engine as done herein has, to our knowledge, not been done before.
In the assemblies of a mobile equipment trailer having certain combinations of equipment that include fluid couplings, allocations of space may be such that it is beneficial to have the reservoir located remotely from, yet at a level below, the bottom flange of the fluid coupling. This can be accommodated with the use of a conduit of sufficient diameter between the bottom flange of the fluid coupling and the reservoir, and with a pump directly driven by an electric motor or a hydraulic motor. Preferably, the inlet to the pump is below the oil level of the reservoir. The pump may be located in the reservoir or separate from the reservoir.